The present invention relates to a supporting element for a housing for a vehicle traction battery as well as to a housing having such a supporting element. The invention further relates to a process of producing a supporting element for a housing of a vehicle traction battery, as well as to a process of producing a vehicle traction battery.
Vehicle traction batteries are used, for example, for the drive of hybrid vehicles or electric vehicles. So that the electric machine installed in such vehicles for the drive can be supplied with the necessary electric power, vehicle traction batteries are designed such that they have a high electric output voltage and, in addition, can provide high electric currents. This is achieved in that a large number of storage cells are mutually connected in a parallel and serial manner.
The vehicle traction battery is usually constructed of a number of power storage modules, each of the power storage modules having a number of storage cells which, as a rule are arranged in a stack, which is braced by way of end plates and tension elements. The storage cells contain electrochemical cells by means of which electric power can be stored.
The required large number of storage cells or power storage modules has the result that vehicle traction batteries usually have a large volume. Because of the limited installation possibilities, a vehicle traction battery is often installed in the area of the underbody of a vehicle, which is why the vehicle traction battery has a low height and therefore a large base (definitely up to 150 cm×100 cm). In order to, on the one hand, protect the vehicle traction battery from external effects and, on the other hand, have a retaining possibility in the event that a malfunctioning occurs during the operation of the vehicle traction battery and, for example, electrolyte and/or gas is released in the process, the vehicle traction battery is built into a housing.
A housing for a vehicle traction battery has a supporting element and a covering element, the power storage module being fastened to the supporting element. So that the housing can carry out the desired protecting function, it has to have specific characteristics or meet specific demands. In particular, the supporting element should have a sufficiently high stiffness and, in addition, be able to easily absorb or distribute affecting forces. This results in demands on the material of which the supporting element is made and on the manufacturing process to be used respectively.
It was found that the die casting process is particularly suitable for the manufacturing of housings for vehicle traction batteries, because this process is generally suitable for mass production and, in addition, housings, particularly supporting elements, manufactured in this manner meet the above-mentioned stiffness requirements and force absorption or force conduction demands. Such housings are preferably constructed as aluminum die castings.
However, it is not unproblematic for large-surface components to be manufactured by means of die casting methods, particularly if large-surface housing supporting elements are to be manufactured as aluminum die castings: In principle, explosive forces occur during a casting operation which act upon the two mold halves and force the latter apart. In this case, the explosive forces depend on the surface of the component to be cast and will rise as the component surface increases. When a component to be manufactured reaches a specified surface and the explosive forces therefore reach a specified value, it will no longer be possible to produce a large-surface component in one piece, i.e. in a single casting operation, by means of a conventional die casting machine. As a result, it would only be possible to produce a large-surface component by using a conventional die casting machine if it were constructively divided in two component halves and these two halves were produced separately. In this case, the separation can take place in the longitudinal or transverse direction. This partitioning reduces the individual surfaces and thereby the explosive forces occurring during the casting operation. The two halves produced in two separate casting operations are mutually connected, for example, by being welded or screwed together.
Even if the explosive forces are reduced and can thereby be controlled by the partition of the large-surface component to be manufactured, the division of the component to be manufactured would have the following considerable disadvantages:
The partition into individual parts interrupts the casting geometry of the large-surface component composed of the individual parts, which has a disadvantageous effect on the stability of the component.
If the large-surface component is a supporting element for a housing for a vehicle traction battery, which, for forming the entire housing, is connected with a covering element, the sealing surface between the supporting element and the covering element would be interrupted and therefore have to be finished at high expenditures, because of the fact that the supporting element is composed of individual parts.
The individual parts are to be mutually connected for forming the large-surface component. Because of the resulting connection points or the connection components used for this purpose, the weight of the overall manufactured large-surface component would increase.
Because all individual parts of which the large-surface component is composed, are constructed as die cast parts, the component as a whole has a uniform high minimum wall thickness, resulting in a high weight of the component.
A separate die casting mold is required for each individual part, which significantly raises the costs for the molds in comparison to a production for which the use of a single die casting mold is sufficient.
As a result of the finishing work, which, on the one hand, is required in connection with the sealing surface and, on the other hand, for connecting the individual parts, the production process is more complex and the manufacturing costs are therefore higher.
As a result of the fact that the finished large-surface component is composed of a plurality of individual parts, it has connection points and separating points respectively, limiting the use of the installation space available inside the housing.
It is therefore an object of the present invention to create a supporting element for a housing for a vehicle traction battery, which can be produced in a simple manner and therefore at lower manufacturing expenditures. It is a further object to create a supporting element which, in addition, has a low weight. It is a further object of the present invention to create a process by which a corresponding supporting element can be produced.
These objects are achieved by a supporting element for a housing for a vehicle traction battery, which is constructed of a module supporting element and at least one closing element which has a plate-shaped design, the module supporting element having a number of module fastening elements, to which a number of power storage modules are fastened, of which the vehicle traction battery is constructed, the module supporting element further having at least one recess which is closed by the plate-shaped closing element.
These objects are further achieved by a process for producing a supporting element for a housing for a vehicle fraction battery, by which the following steps are carried out:
Providing a module supporting element which has a number of module fastening elements and at least one recess,
Providing at least one closing element of a plate-shaped design,
Closing the recess by means of the plate-shaped closing element.
Although the following statements relate to the die casting process or to a supporting element produced by a die casting process, this should not have any fundamental limiting effect. The approach according to the invention can also be used in other production processes; particularly those in which the manufacturing of large-surface components, particularly the production of supporting elements, may present problems. Correspondingly, this also applies to the material of which the supporting element is made. However, the approach according to the invention was worked out on the basis of the above-described explosive—force-related problem existing in the die casting process, therefore resulting, according to current knowledge, in the greatest advantages in the case of this production process.
As a result of the fact that the supporting element has at least one recess, which, in particular, is further developed having a large area, the surface of the supporting element to be produced, more precisely, the area of the module supporting element, is reduced to such an extent that the explosive forces occurring in a casting operation are reduced to such an extent that the supporting element can be produced in one piece, i.e. in a single casting operation; i.e. the module supporting element can be manufactured by using a single mold consisting of two mold halves. Advantageously, the supporting element is constructively divided and designed such that the module supporting element essentially takes over the supporting or bearing function; i.e. the power storage elements are fastened to the module supporting element. The module supporting element therefore represents a bearing structure, whereas the plate-shaped closing element only carries out a closing and thereby enveloping function. In the case of the supporting element according to the invention, the recess is arranged such that, in the unclosed condition, it represents an opening of the vehicle traction battery with respect to the environment. The closing element may be constructed such that the power storage modules are slightly supported on the latter; for example, in that the power storage module is braced by means of a cooling body arranged between the closing element and the power storage module.
The partitioning of the supporting element into a module supporting element, which has a supporting or bearing function, and into a plate-shaped closing element, which essentially has an only enveloping or closing function creates the greatest possible design freedom. This permits the design of a module supporting element whose casting geometry is not interrupted, so that the stability of module supporting element as well as of the supporting element will not be limited. It is thereby also ensured that the supporting element permits a continuous distribution of power, which results in an optimal voltage distribution without any voltage jumps. Furthermore, as a result of a correspondingly suitable definition of the location of the recess, care can be taken that the sealing surface between the supporting element and the covering element will not be interrupted, whereby costly finishing work can be eliminated and the production process will be cost-effective, which will result in lower manufacturing costs. Particularly the sealing geometry will be simplified and thereby more advantageously presentable. Furthermore, the suitable defining of the location of the recess can achieve the following: On the one hand, the expenditures for the refinishing for connecting the individual parts—in this case, for connecting the module supporting element and the plate-shaped closing element—will be lower, which also leads to a reduction of the complexity of the manufacturing process and thus of the manufacturing costs. On the other hand, the connection points between the module supporting element and the closing element can be constructed more cost-effectively or simpler connection components can be used, which both results in a reduction of the weight and of the manufacturing costs of the supporting element. In addition, because of the advantageous selection of the location of the recess, the location of the connection points or separating points can be placed so advantageously that the utilization of the installation space available in the housing will only be insignificantly limited. The available installation space therefore does not have to be used for a connection flange of the two component halves created by longitudinal or transverse division but can be used for the design stiffness of the supporting element. When the module supporting element as well as the plate-shaped closing element are produced by the die casting process, although two mold sets are also necessary, specifically one for the module supporting element and one for the closing element, because the mold set for the closing element is significantly less complex because of the simple geometry of the closing element, the mold-related costs are reduced in comparison to the division of the supporting element in the longitudinal or transverse direction practiced up to now.
A supporting element is thereby created which, while taking into account the mechanical demands, is, on the one hand, optimized with respect to costs and, on the other hand, with respect weight. The optimization with respect to weight will even exist when the module supporting element as well as the closing element are produced of the same material and according to the same manufacturing process respectively.
It should be mentioned at this point that the recess is a large-area recess, which is clearly larger than a recess as provided for the accommodation of a screw, by means of which a power storage module or another component is fastened to the supporting element. The fraction of the recess with respect to the surface of the supporting element, in which the recess is situated, may definitely be in the order of 10 to 20%.
The above-mentioned object is therefore fully achieved.
With respect to the weight reduction, the supporting element can be further optimized, specifically in that the module supporting element and the closing element differ at least with respect to one component parameter. Such a parameter is to characterize the material used for the manufacturing of the respective element or the respectively used manufacturing or production process. In a particularly preferred further development, the module supporting element is a die-cast part, particularly a die-cast aluminum part, and the plate-shaped closing element is a metal plate. The metal plate may consist of aluminum or steel and may be produced, for example, by a stamping or laser-cutting operation. As a result of the fact that the recesses are closed by a metal plate or a sheet-metal plate, the supporting element will no longer have a continuously uniformly high minimum wall thickness, which results in a clear weight reduction. A weight-optimized supporting element can thereby be produced without any loss of stability or stiffness. Since the production of metal sheets is much easier than that of a die-cast part, a supporting element constructed in this fashion also has very low manufacturing costs. As a result of this hybrid construction method, the advantages offered, on the one hand, by the die casting and, on the other hand, by the use of plate-shaped sheet metal elements are mutually linked. As an alternative, instead of the metal sheet, a closing element can be used that is made of a plastic material.
As mentioned above, a housing for a vehicle traction battery has a supporting element and a covering element, in which case there are several implementation options. The covering element may therefore be a separate component, so that after the connection of the supporting element with the covering element, the housing will be separate with respect to the vehicle body. As an alternative, the covering element may be a component of the vehicle body, such as a metal plate arranged in the area of the vehicle underbody or of the vehicle trunk. After the connecting of the supporting element and the covering element, the housing is fixedly connected with the vehicle body and is therefore not separate with respect to the vehicle body. Furthermore, in the case of the housing installed in the vehicle, in a first further development, the covering element may be the top part of the housing and the supporting element may be the bottom part of the housing, while, in a second further development, the covering element may be the bottom part of the housing and the supporting element may be the top part of the housing. The above-described alternatives may be combined with one another, so that a total of four variants of further developments are obtained. The following implementations are based on the variant of a further development in which the covering element is constructed as a separate component, and the supporting element represents the housing bottom part and the covering element represents the housing top part, in which case, the above should not have a limiting effect.
In a further development of the invention, the recess is essentially arranged below at least one fastened power storage module. As a result of this measure, a considerable freedom of design is obtained for the arranging of the recess, because a large area is available below the fastened power storage module within which a large-area recess can be placed without thereby impairing the supporting function of the supporting element. For the supporting element, a clear explosive force reduction can thereby be obtained, on the one hand, with respect to the die-casting process and, on the other hand, a clear weight reduction can be achieved.
Corresponding to a further development of the invention, the number of module fastening elements can consequentially be arranged such that the fastened power storage modules are arranged in a number of rows of power storage modules, the recess and the plate-shaped closing element being in each case designed such that, with respect to their dimensions, they essentially correspond to a surface that is covered by one row of power storage modules. This clearly achieves a reduction of explosive force and weight.
In a particularly preferred further development of the invention, the number of module fastening elements is arranged such that the fastened power storage modules are arranged in a plurality of rows of power storage modules, a recess being arranged below each row of power storage modules. The explosive forces and the weight of the supporting element can be reduced most effectively by this measure.
In a further development of the invention, the module supporting element further has a receiving element encompassing the recess, the receiving element having a bearing area and a the receiving area offset with respect to the bearing area, the closing element being glued to the module supporting element by way of an adhesive arranged in the receiving area. The gluing-together is an inexpensive and cost-effective connecting method for mutually connecting the module supporting element and the closing element. In addition, if preferably an adhesive with a sealing characteristic is used, a gas-tight closure of the housing can be achieved.
For securing the connection of the module supporting element and the closing element, in a further advantageous development of the invention, the bearing area has a number of element fastening holes by way of which the closing element is screwed to the module supporting element. On the whole, the module supporting element and the closing element are mutually connected by being glued and screwed together; i.e. a connecting technique is used that is easy to carry out, whereby the manufacturing costs for the supporting element can be kept low. In addition, the connection elements do not have excessive weight, whereby the weight of the supporting element can be kept low. The supporting element can therefore be produced by simple working steps, specifically, applying the adhesive, placing the closing element in the recess of the module supporting element and screwing-together the closing element and the module supporting element.
As an alternative, the supporting element and the closing element can also be mutually connected by riveting or welding.
While using a supporting element as described above, a vehicle traction element can be produced corresponding to the following process steps:
Providing a supporting element, which is constructed of a module supporting element and at least one plate-shaped closing element, the module supporting element having a number of module fastening elements and at least one recess, which is closed by means of the plate-shaped closing element,
Providing a number of power storage modules,
Fastening the power storage modules to the module fastening elements, and
Connecting the supporting element with a covering element.
Embodiments of the invention are illustrated in the drawing and will be explained in detail in the following description:
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.